The means whereby near UV-light leads to cytotoxicity in the ocular tissues are being explored from three aspects. These include: 1) Experiments designed to observe the chemical and physical changes induced in human (and rabbit) lens proteins by exposure of the cultured lenses to near-UV light. To enhance the reaction, tryptophan will be added to the medium; to inhibit the action of the light, ascorbic acid will be added. 2) Effects of near-UV light on the lens and retina of guinea pigs will be explored by housing young animals under black light or under incandescent light for six-to eight months, while feeding them excesses of ascorbic acid to inhibit tissue damage and excesses of riboflavin to enhance tissue damage. 3) Tryptophan photoproducts will be isolated and characterized; the most inhibitory product for cell growth will be found, and its mechanism of action in the inhibition of macromolecules of various cell types, including lens epithelial cells, will be explored.